1. Field of the Invention
The present invention relates generally to an inspection apparatus. and more particularly to an inspection apparatus suited for detecting marks formed on a sample surface.
2. Description of Background Art
In usual, ID numbers (marks) are formed on a surface of each semiconductor wafer identifying for example a type of product and a name of customer in order to manage the manufacturing process of semiconductor using the marks. The ID numbers are conventionally read with the naked eye of an operator.
The ID numbers are formed on the semiconductor wafer near the orientation flat thereof. A portion near the orientation flat is a region in which a pattern of circuits or wiring is not usually formed and thus no film of insulation or conductor is coated. Accordingly, it is usually possible to read the ID numbers by the naked eye. However, in a occasional case in which some pattern would be formed near the orientation flat, or in a case in which the ID numbers would be coated by a resist film for a pattern formation due to a position shift of the pattern during the pattern forming step and other reasons, substantial time is required for reading the ID numbers since lights scattered by the pattern and the resist surface detract the visibility of the ID numbers.
On the other hand, although there is another inspection apparatus in which the ID numbers Are read by using an optical system, it is very difficult to read the ID numbers if they are coated by any film coating.